1. Field of the Invention
This invention relates to a heavy duty crane capable of hoisting ultra heavy loads.
2. Description of the Prior Art
Heavy duty cranes of this class usually employ a couple of mobile and swivellable base units which correspond to the base machine of an ordinary crane and which are connected with each other by a link frame, a boom mounted on one of the base units, a counterweight mounted on the other base unit, and a gantry provided across the two base units to interlink travelling and swivelling movements of the two base units. Such super size cranes are originally intended for operations of hoisting ultra heavy loads in a large open place, without giving much consideration to quick response in turning and travelling operations nor to the large operating ground space necessitated by a crane. However, as a matter of fact, they are not always used for hoisting ultra heavy loads which require their full capacities but are often used for handling smaller loads. In such a case, the lack of quick response in operation and the large operating ground space, which are inherent in a heavy duty crane, become hindrous in operation. More specifically, for turning a heavy duty crane, one base unit is moved around the other base unit, and, for moving the same for relocation, the two base units need to be simultaneously moved in the same direction at a uniform speed. These operations have to be performed carefully in a very elaborate and inefficient manner by a number of operators who closely communicate with each other. Moreover, the distance between the centers of the two base units measures about 36 meters in some cases and the crane as a whole extends over a distance of about 50 meters, requiring a very large operating ground space which is difficult to secure under some circumstances.